1. Field of the Invention
Aspects of the present invention relate to a cap assembly, and a secondary battery using the cap assembly, to prevent an increase of internal resistance, and to increase the capacity of the secondary battery, per unit area.
2. Description of the Related Art
Recently, as portable electronic devices, such as, cellular phones, notebook computers camcorders, etc. have been widely distributed, the secondary battery has actively been developed for use as a power source of these electronic devices.
Secondary batteries can be classified as Nickel-Cadmium (Ni—Cd), Plumbum (Pb), Nickel-Hydrogen (N—H), Lithium ion, Lithium Polymer, and so on. Lithium secondary batteries have been widely used in electronic devices, because such batteries can be compact, and can have a large capacity, a high operating voltage, and a high energy density per unit weight.
Lithium secondary batteries can be divided into a can-type and a pouch-type, according to the shape of a casing containing an electrode assembly. The can-type batteries can be prismatic or cylindrical.
A cylindrical secondary battery comprises: an electrode assembly; a can to house the electrode assembly; and a cap assembly including an insulating gasket, to seal an opening of the can. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. An electrolyte is also contained within the can.
The cap assembly may be formed by sequentially stacking a cap-up, a current interrupt device, a positive temperature coefficient (PTC) thermistor, and an electrode terminal, in the opening of the can. The cap assembly may be formed by combining the cap-up, with other elements as a unit, and then sealing the opening of the can with the cap assembly.
Recently, an integrated configuration of the electrode assembly has been proposed, in order to simplify manufacturing, and to reduce any contact resistance of the components. Caulking and welding methods have been widely used to form the integrated configuration. With the welding method, however, it is very difficult to form an integrated configuration including a cap-up, since the PTC thermistor, whose characteristics are changeable by heat, is disposed between the cap-up and the current interrupt device.